Angiogenesis, the formation of new blood capillaries from preexisting vessels, is essential for normal physiological processes, such as wound healing and embryogenesis. It also occurs under pathological conditions, such as cancer, rheumatoid arthritis, and certain cardiovascular diseases. Vessel formation is a complex event controlled by multiple signaling pathways activated by angiogenic factors and by endothelial cell-matrix interaction. p38 MAP kinases are activated by angiogenic factors and by extracellular matrix proteins. Both in vivo and in vitro studies have shown that the p38 signaling pathway plays important roles in the regulation of angiogenesis. However, the mechanisms involved are not well defined. The goal of this research is to investigate the roles for p38alpha and p38beta, two major isoforms expressed in endothelial cells (ECs), in the regulation of EC activities involved in angiogenesis. To accomplish this goal, we will modulate the expression level and kinase activity of p38alpha and p38beta by adenovirus-mediated gene targeting technique. The specific functions of p38alpha and p38beta will be assessed in two different experimental systems: a) in 2-dimensional (2D) cell dishes where cell proliferation is the major activity of ECs, and b) in 3D collagen matrices where ECs differentiate into tube-like structures, mimicking the steps of vessel formation. The specific aims of this project are: 1) to test the hypothesis that angiogenic factors (bFGF and VEGF) and collagen matrix differentially activate p38alpha and p38beta, which may coordinately regulate vessel formation, 2) to determine the roles of p38alpha and p38beta in EC proliferation, survival, and morphogenesis, and 3) to test the hypothesis that the p38 pathway may serve as a molecular switch between proliferation and differentiation in 2D and 3D cell culture environments. We expect that the results obtained from the two different experimental systems will be complementary and lead to a better understanding of the signaling mechanisms of p38alpha and p38beta in the regulation of angiogenesis. This investigation may provide new knowledge to the development of novel therapeutic drugs for diseases associated with angiogenesis.